Hitherto, reversible solenoids were constructed in one of three ways: those having (1) solid round armature magnetized radially, (2) a hollow armature magnetized radially or (3) a solid armature over which a magnetized annular ring is placed. Each of these methods has its own distinct problems which become amplified as the size of the solenoids is reduced. With respect to the first method, it is very difficult to magnetize a solid round rod radially; as to the second and third methods, the size of the solenoid is limited to the size of the magnetizing coil which must be inserted in the bore of the armature or annular ring.